1. Field of the Invention
The present invention relates to a vacuum extraction apparatus and process for multi-phase extraction.
2. Background Discussion
The major problems associated with the existing multi-phase extraction (MPE) inventions are twofold:
I) The existing inventions cannot adjust to changes in water levels that are below 25 feet below grade level (bgl) without sacrificing simplicity, efficiency or effectiveness. PA1 ii) The present prior art inventions typically embody a complicated connection between the air inlet port and the internal drop tube well casing, that makes it substantially more difficult and expensive to construct and adjust.
3. Summary
At many industrial and commercial facilities and at waste handling and disposal sites, soil and groundwater are contaminated with chemicals adsorbed in the soil and dissolved in the groundwater. A variety of techniques have been used for removal of soil contaminants and remediation of affected soil. One common technique involves the excavation and off-site treatment of the soil. Another technique involves saturating the contaminated soil with water in situ, causing the contaminants to be slowly leached from the soil by the water. The contaminated water can then be removed.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. Typically, a vacuum is applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is less dense than water, would float on the water table and present a layer which could be drawn off by vacuum applied to the liquid at or around that level. Another prior art scheme, exploits two phase vacuum extraction, a single vacuum device removes contaminants in both the water and the soil gases by way of a single conduit formed by the well casing. However, none of the foregoing systems are designed to effectively accommodate variations in the groundwater level, and operate substantially beyond conventional vacuum limits, while retaining the simplicity and cost effectiveness of standard vacuum extraction systems.
Others have suggested the possibility of venting soil above the water table (i.e., in the vadose zone) to cause volatilization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Thus, conventional vacuum extraction systems are designed to remediate the vadose zone by applying vacuum to draw air to the soil through wells having screening which does not extend below the water table.
It would be desirable to provide an apparatus and process to overcome these limitations. More specifically, it would be desirable to provide an apparatus and process that can effectively accommodate variations in the groundwater level. Further, it would be of great advantage to provide an apparatus and process that maximizes drawndown of groundwater in a well and enables effective operation substantially beyond conventional vacuum limits while retaining the simplicity and cost effectiveness of standard vacuum extraction systems.
Contaminants can exist in subsurface soil and groundwater in a non-aqueous phase liquid adsorbed to soil and mixed with and/or dissolved in groundwater and soil gases. Various contaminants can be found in groundwater and soil, such as volatile compounds, including volatile organic compounds, nonvolatile materials, metal contaminants, and the like. Such contaminants can be found and remediated in the vadose (unsaturated) zone found between the surface of the search and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
At many industrial and commercial facilities and at waste handling and disposal sites, soil and groundwater are contaminated with suspended or water-soluble chemicals or both. A variety of techniques have been used for removal of contaminants and remediation of affected soil. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
Further exemplary of these techniques are the following United States Patents. They are incorporated herein in their entireties and cited in greater part to enable the person of ordinary skill to practice the instant invention.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. For example, in U.S. Pat. No. 4,323,122, as noted above, it was proposed that a vacuum be applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is less dense than water, would float on the water table and present a layer that could be drawn off by vacuum applied to the liquid at or around that level. U.S. Pat. No. 4,323,122 (Knopik) discloses a system and method for recovering organic liquid such as gasoline which has settled on the water table in underground areas. The systems comprises a conduit extending from the ground surface to a point just above the water table, a collection head fitted on the lower end of the conduit, a collection vessel connected to the upper end of the conduit, and an exhaust means for creating less than atmospheric pressure in the vessel. The collection head has a liquid impermeable end portion and a liquid permeable intermediate portion for permitting the passage of liquid. The process comprises providing an opening in the ground to a point beneath the surface of the water table, positioning the conduit with the collection head in place so that the liquid permeable wall of the collection head is just above the surface of the water table, connecting the conduit to the collection vessel intake, and exhausting air and other gaseous materials from the vessel to cause liquid to flow into the collection head through the conduit into the vessel.
Through a method called soil-vapor extraction, others have suggested the possibility of venting soil above the water table (i.e., in the vadose zone) to cause vaporization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Through another method called vacuum enhanced groundwater recovery, groundwater requiring treatment is in such processes conventionally removed by pumping from separate conventional water wells. In situations in which water does flow into vacuum extraction wells, it has been suggested that a second, liquid phase pump be placed either in the well or at the surface to remove the water through a second conduit. For example, U.S. Pat. No. 4,660,639 (Visser et al), the disclosure of which is totally incorporated herein by reference, discloses a process for the removal of volatile contaminants from the vadose zone of contaminated ground by extracting volatilized contaminants from the vadose zone by way of one or more vacuum extraction wells. The process entails drilling one or more wells into the subsurface media in the contaminated area, the well being constructed so that fluids in the vadose zone can flow into the well, whereas the liquid in the saturated zone below the water table cannot substantially flow into the well. The borehole and conduit of the well can optionally extend below the water table, in which case the vacuum applied to the upper portion of the conduit will be effective to draw contaminant from the vadose zone, but insufficient to draw a significant amount of water from the saturated zone into the conduit. If it is desired to remove groundwater from below the water table, this removal is accomplised either by a separate sampling device situated in the borehole or through a separate well.
In addition, Stinson, "EPA Site Demonstration of the Terra Vac In Situ Vacuum Extraction Process in Groveland, Mass", Air & Waste Management Association, Vol. 39, No. 8, pages 1054 to 1062 (1989), the disclosure of which is totally incorporated herein by reference, discloses an evaluation of an in situ vacuum extraction process. The process entails removal of contaminants from the vadose zone by vacuum. Wells are installed in the contaminated soil located above the watertable. A vacuum pump or blower induces air flow through the soil, stripping and volatilizing volatile organic compounds from the soil matrix into the air stream. Liquid water, if present in the soil, is also extracted along with the contamination. The stream of contaminated air and water flows to a vapor/liquid separator where contaminated water is removed. The contaminated air stream then flows through a treatment system such as gas-phase activated carbon to remove contaminants from the air stream. The clean air is exhausted to the atmosphere through a vent. U.S. Pat. No. 4,593,760 (Visser et al) the disclosure of which is totally incorporated herein by reference, and U.S. Reissue Pat. No. Re. 33,102, the disclosure of which is totally incorporated herein by reference, also disclose processes for removal of volatile contaminants from the vadose zone of contaminated ground by pumping volatilized contaminants from the vadose zone using one or more vacuum extraction wells.
U.S. Pat. No. 5,709,505 discloses a process for removing contaminants from a contaminated area of the subsurface which comprises providing a borehole in the contaminated area; placing in the borehole a perforated riser pipe inside of which is situated a vacuum extraction pipe with an opening situated within the perforated riser pipe, wherein a packing is situated in a portion of the annular space between the vacuum extraction pipe and the perforated riser pipe; applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the subsurface into the perforated riser pipe below the packing and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and removing contaminants from at least one of the liquid stream and the gaseous stream. Also disclosed is an apparatus for carrying out the disclosed process.
U.S. Pat. No. 5,076,360 (Morrow), disclosure of which is totally incorporated herein by reference, discloses methods and apparatus for vacuum extraction of contaminants from the ground which, in a preferred embodiment, entails vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluent. A primed vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing utilizing a priming tube which introduces air or other gas to the liquid collected at the bottom of a well. The method permits vacuum extraction of both liquids and gases from the subsurface by way of wells having a liquid layer which is more than thirty feet below the soil surface or in which a screened interval of the extraction pipe is entirely below the liquid surface.